The method of the present invention comprises reacting a siloxane having silicon hydride functionality and at least two repeat units, at least one of which has the formula ##STR1## where R is an organo group and a is 1 or 2, with beta(allyloxy)ethyl methacrylate in the presence of an amount of hydrosilation catalyst effective for catalyzing a hydrosilation reaction between the allyl group on said methacrylate and said silicon hydride functional siloxane. Preferably the siloxane compound with silicon hydride functionality is a polyorganosiloxane with a molecular weight of 2500 or more, suitably 20,000 or more. Preferred organo groups are hydrocarbon groups such as methyl and phenyl groups. Other typical organo substituents for siloxane polymers, such as trifluoropropyl, methoxy or acetoxy groups may also be included.
This invention relates to polyorganosiloxane polymers (silicones) which have methacrylate functionality thereon.
Methacrylate functional organosiloxane compounds and polymers are desirable because they have faster and more versatile free radical cure characteristics than do the commercially available vinyl silicones. As described in U.S. Pat. Nos. 2,956,044 and 4,035,355, methacrylate functional silicones can be formulated with other unsaturated monomers to give monomer compositions or cured polymers with unique and desirable properties. U.S. Pat. No. 4,035,355 describes anaerobically curing compositions of methacrylate functional siloxane polymers. U.S. Pat. No. 3,577,264 describes radiation curable film-forming paint binders utilizing acrylate or methacrylate functional siloxanes. Other patents describing methods of preparation or uses for methacrylate functional siloxanes include U.S. Pat. Nos. 2,793,223; 2,898,361; 2,922,806; and 2,922,807, and 4,348,454 and U.K. Pat. Nos. 1384898 and 1323869.
In U.K. Pat. No. 949,126 there are described hydrolyzable silane compounds used as adhesion promoters for glass fiber reinforcing materials, some of which are prepared by hydrosilation of allyl-functional methacrylates such as allyl-methacrylate and beta(allyloxy)ethyl methacrylate. However, hydrosilation of allyl-substituted compounds has elsewhere been observed can be complicated by competing side reactions such as propene elimination unless the reacting silicon hydride contains strong electron withdrawing groups such as chlorine or carboxyl. See Speier, J. L., et al., J. Am. Chem. Soc., 79 1974 (1957); and Ryan, J. W., et al., J. Am. Chem. Soc., 82, 3601 (1960).
In U.S. Pat. No. 3,878,263 there are described acrylate and methacrylate functional siloxanes prepared from hydrolyzable acrylic functional silanes. The silanes may be prepared by hydrosilation of acrylic esters of unsaturated alcohols. Alternatively, the silanes may be prepared by reacting an alkoxy or hydroxy chloroalkyl silane with a tertiary amine salt of acrylic or methacrylic acid.
It is possible to prepare methacrylate functional silicones by hydrosilation of allyl methacrylate with silicon hydride functional polyorganosiloxane polymers, but, consistent with published reports on allyl hydrosilations, it has been observed that the process consistently yields a product in which about 30% of the methacrylate groups grafted onto the polymer are hydrolyzable. These groups are believed to have the following structure (where the hydrosilating groups were methylhydrosiloxane groups). ##STR2## The presence of these hydrolyzable methacrylate groups produces a number of problems when the polymer is exposed to moisture, including loss of methacrylate functionality and increase in viscosity of the uncured polymer due to siloxy crosslinking.
The problem of propene elimination when allyl esters are hydrosilated is also recognized in U.S. Pat. No. 3,767,690 to Speier where organosilicon cinnamates were prepared from allyl cinnamates and organosilicon compounds which have mercapto functionality instead of SiH functionality.
When methallyl methacrylate is substituted for allyl methacrylate the propene elimination problem is eliminated but hydrosilation occurs at both ends of the molecule. ##STR3##